A quick-footed thief punched a man on the R train at the Canal Street station at about 6 p.m. on June 22, then sprinted off with his victim’s iPhone, cops said.

The victim, a bald man wearing a suit, chased the thug into a full-height turnstile and trapped him with help from two other commuters for about 20 seconds, NYPD video shows. The shirtless crook then threw himself against the metal bars until he could squirm free and flee.